This invention relates to a gas leak detector, and more particularly to a gas leak detector capable of detecting a trace amount of gas leak from a variety of equipments, piping systems and the like and suitable for use in locating leak points.
Halogenated hydrocarbon gas has been widely used as refrigerant gas or coolant for electric refrigerators, air conditioners and the like. Halogenated hydrocarbon has a chemical formula wherein one or more of the hydrogen atoms has been replaced by chlorine, fluorine or the like, and typically includes R-12(CCl.sub.2 F.sub.2), R-22 (CHClF.sub.2), etc. These halogenated hydrocarbons are chemically and thermally very stable, harmless to human bodies, and have excellent thermodynamical characteristics when they are used for refrigeration systems.
In the refrigeration systems, the halogenated hydrocarbon gas mentioned above is alternately compressed and expanded to cause its refrigeration actions. At this time, a trace amount of the halogenated hydrocarbon gas may sometimes leak away from compressors, radiators, pipes, etc. If such leaks are left unstopped, efficiency of the refrigeration systems is lowered due to a gradual decrease of the refrigerant gas, with the result of a possible cessation of the function of such equipment. Accordingly, stringent control is required when such equipment is manufactured in a factory, and it is desirable to periodically check any leak along the pipe systems. Especially, in the refrigeration systems such as air conditioners for cars and the like, there is a greater possibility of leak due to a shock during drive, and a detector which may simply find out the leaks has long been desired.
Generally, the air conditioner as mentioned above is heavy in weight, and in addition it is usually fixed at one place or mounted on a car. Therefore, it is impossible to make an inspections thereof by simply turning or overturning it. Moreover, the leaks are usually too small to find out visually or by a magnifier. Further, it is desirable for a leak detector to be as miniature as possible since the pipe system, etc. is usually of complicated structure. Still further, the detecting end of a detector should preferably be as small as possibile in diameter since the detector traces the pipe or the like to locate a leak. In addition, it is required that a detector can be operated by means of a miniature cell or cells in order to make it easy to handle. While the sensitivity of a detector is desirably as high as possible as a matter of course, it is required for it to detect a gas leak of at least 10.sup.-4 cc/sec (25.degree. C., 1 atm).
There has been proposed a number of halogenated hydrocarbon gas detectors, some of examples of which are explained below:
A typical detector, a torch, utilizes a kind of flame reaction; it utilizes the phenomenon that the color of flame changes responding to the chemical reaction of the halogen gas mixed into the flame with a copper metal provided in the flame. Although this method is simple, it is often accompanied by errors because the presence or absence of leaks is visually judged. Moreover, the limit of detection according to this method is 10.sup.-2 cc/sec (25.degree. C., 1 atm) at best.
Further, there has been proposed a detector which utilizes high voltage electric discharge. This detector is provided with a pair of electrodes exposed to air with a gap therebetween, to which electrodes is applied a high voltage of several hundred volts for producing an electric discharge at the gap. The discharge stops when halogenated hydrocarbon gas comes into the gap between the electrodes. As a result, the leak can be detected by detecting the change of the discharged current, with the detection limit leveled up to 10.sup.-3 cc/sec (25.degree. C., 1 atm) which is sufficient for practical use. However, this detector, which utilizes the electric discharge, is disadvantageous in for example that the discharge is interrupted due to other external causes such as wind or the like even when there is no leak of the halogenated hydrocarbon gases.
On the other hand, as a detector having sufficiently high sensitivity, there has been known a detector called a cation emission type leak detector. The detector of this type comprises ceramics containing Na, K, etc., an ion collector electrode and a heater. The ceramics are heated to a high temperature (e.g. 800.degree. C.), to which ceramics there is provided at a predetermined space an ion collector electrode made of a metal. While a high voltage of about 300 V is applied to the space between the ceramics and the ion collector electrode, the halogenated hydrocarbon gas is reacted on the surface of the ceramics due to the high temperature to emit ions of Na, K, etc. contained in the ceramics, which ions are attracted to and captured by the metallic electrode with the aid of the high voltage. As the result, the leak can be detected by detecting ionic current thus generated. According to this detector, the detection limit is not more than 10.sup.-6 cc/sec (25.degree. C., 1 atm) and thus the detector exhibits very high sensitivity.
However, the detector of this type consumes the electric power of as large as 20.about.30 W because the ceramics must be kept at a high temperature (about 800.degree. C.) as mentioned above, whereby not only a larger size of an apparatus but also a cord for the power source are required, and also the detector must be of a larger size for the same reason. In addition, such a detector is necessarily expensive because a metal such as platinum which is resistant to a high temperature must be generally used as the material for an electrode.
As a gas leak detector making use of an oxygen-ion conductive solid electrolyte, there has been known a gas leak detector in which a pair of electrodes are provided respectively on both surfaces of a plate-like oxygen ion conductive solid electrode and a porous oxydizing catalyst which can oxidize flammable gases such as CO gas, propane gas and the like, is applied on the surface of one of the electrodes (Japanese Patent Laidopen Application No. 146,690/1979). The aforementioned gas leak detector is certainly effective in finding an average gas concentration in the surrounding atmosphere, but it is extremely difficult for such a conventional gas leak detector to detect gas leakage, particularly, from a minute crack or hole.